A prerequisite for accurate invasive arterial pressure measurement is familiarity with measurement principles and pitfalls. Using an electronic survey, we assessed knowledge about invasive arterial pressure monitoring and current invasive arterial pressure monitoring practices in the ICU. The questionnaire was sent to nurses and physicians who are members of the French Intensive Care Society and the Réseau Européen de Recherche en Ventilation Artificielle network. Three hundred nine nurses and 76 physicians responded. We identified considerable gaps in knowledge and differences in practices that can significantly impact the reliability of invasive arterial pressure measurement, mainly the confusion between zeroing and leveling the transducer and the heterogeneity in external landmarks choice for the phlebostatic axis. In modern critical care, where mean arterial pressure targets are recommended and where patients are awake and/or frequently mobilized, standardized invasive arterial pressure monitoring is required.